In the manufacture of apparel, particularly knitted fabrics, once greige goods have been knit, they are inspected and transferred to a finishing line where one or more types of finishing operations are undertaken. During finishing, the goods may be bleached or dyed in preparation for cutting. Some fabric constructions, such as knitted fabrics, are not dimensionally stable, that is, their stitch density or width, for example, may vary based on machinery, knit type, material type, and other factors. Thus, knitted fabrics are typically subjected to mechanical compacting to dimensionally stabilize the fabric before it is cut into garment pieces.
Knitted fabric webs typically undergo two separate processes to dimensionally stabilize the web, width setting and compacting. While both processes may be performed by the same machinery, which is generally referred to as a compactor, the two processes will be discussed separately.
In general, width setting is accomplished by a fabric compacting system that includes a mechanical spreader for spreading the fabric web to a preset width. A pair of heated rolls then set the fabric web to the width created by the mechanical spreader. If there was little variability in finished fabric, all that would be necessary would be to set the width of the mechanical spreader and run a trial length of fabric web, make a measurement of the width of the compacted fabric, and make a single adjustment of the width of the mechanical spreader. However, the stitch density and/or width of a fabric web may both vary within a batch of fabric.
Variations occur because of the differing machine, knit type, material type, and counts per inch that are specified by fabric and garment designers. Variations also may occur in connection with the finishing process, including, variations caused by mechanical compacting and even processes that occur downstream from the mechanical compacting process. Accordingly, because of such variations, it is necessary to constantly monitor the width and/or stitch density of the fabric web exiting the compactor, and make appropriate upstream adjustments. Unfortunately, however, it is difficult for a human operator to make accurate adjustments to a fabric web exiting a compactor at speeds approaching about 80 yards per minute.
A number of control systems have been developed to monitor and control the width of compacted fabric. These systems have typically included optical measurement devices, such as cameras, that interconnect a controller to the compactor. For example, control systems have been used for direct measurement of a fabric web as it leaves the compactor. It has been found, however, that there is often no consistent relationship between the width of the fabric web entering the mechanical spreader and the width of the fabric web exiting the compactor. As a result, the prior art control systems tended to oscillate out of control as the control system tried to correct errors that were not, or were no longer, the cause of the variation.
One known control system attempted to solve the oscillation problem by using an image camera to capture images of the moving fabric web as it exited the compactor. While the system was able to detect relatively small changes in the width of the fabric web, problems remained in producing compacted fabric of consistent width because of processing that occurred downstream from the compactor.
In addition to producing a fabric web of consistent width, another objective of compacting fabric is shrinkage control. It is known to compress the knitted courses of a fabric web in the lengthwise direction, which imparts predictable shrinkage to the fabric. The fabric web enters the compactor via a feed roller, which is at a selected speed. The fabric then is rolled between the retard roller and a blade, which is rotating at a slightly slower speed than the feed roller. This causes the fabric to compact, so that the web exiting the compactor is dimensionally shorter in the lengthwise direction than the web entering the compactor. In order to control the compaction process, it is necessary to monitor the stitch density, i.e., counts per inch (CPI), of the compacted fabric.
With respect to the monitoring and control of stitch density, conventional techniques have predominantly involved manual counting procedures whereby random samples of the fabric web are examined under magnification lenses. Other known techniques have involved taking optical measurements during fabric formation or during the fabric treatment process. Like known system and methods of width control, however, a reliable system and method to control stitch density has proven to be elusive because of what are now believed to be changes in fabric stability that occur downstream on the exit conveyor of the compacting machine.
Thus, there remains a need for a system and method for ensuring consistent width and stitch density for a fabric web being finished at high speeds that overcomes the disadvantages of the prior art.